Abstract:
Compared to conventional arc welding processes, laser metal deposition is a low heat input,
low dilution welding process. Weld overlay of thin wall components can be done successfully
with low distortion and low dilution, resulting in the proper chemical composition of the weld
overlay. Refurbishment of cast steel and cast iron components can be done with greater success
resulting in a significant lower tendency towards porosity, weld metal solidification cracking
and heat affected zone cracking. Accurate control of welding parameters results in highly
repeatable weld deposition. Positional welding can be done without difficulty due to the
relatively small spot size.
Laser metal deposition with powder as consumable is a non-contact process and allows for
weld overlay across surface discontinuities. Residual magnetic effects in the substrate do not
influence laser metal deposition in terms of arc wander as compared to arc welding processes.
Undercut in the weld toe does not occur with optimised laser material processing parameters
and weld repair on final machined surfaces can be done successfully. Due to the non-ionising
radiation, porosity formation due to nitrogen absorption is not possible. The same is expected
to apply to hydrogen and as a result, the risk for hydrogen cracking is dramatically reduced for
chromium-molybdenum-vanadium steels.
This study was based on three experimental martensitic deposits containing between 10.5 and
14% chromium, 1 to 6% molybdenum and 0 to 11% cobalt, with the steels with a higher
molybdenum and cobalt content containing less carbon. The nickel content was constant at 5%.
Nominal chemical composition of the low carbon (< 0.03%) martensitic stainless steel alloys
were: 14Cr-5Ni-1Mo (alloy B), 11Cr-5Ni-3Mo-5.5Co (alloy C), 10.5Cr-5Ni-6Mo-11Co (alloy
D). 316L austenitic stainless steel, with nominal chemical composition 18Cr-10Ni-2.5Mo
(alloy A), served as the reference alloy for pitting corrosion resistance.
Laser metal deposition of low-carbon martensitic stainless steel with addition of 1, 3 and 6%
molybdenum was shown to produce fully martensitic microstructures in the as-welded
condition. Rapid solidification of the weld pool suppressed the formation of delta ferrite and
resulted in refined microstructures and improved mechanical properties. Fully martensitic
microstructures were demonstrated by bulk X-ray diffraction. The absence of delta ferrite in
the as-welded condition was confirmed by electron back-scatter diffraction for all three steels.
